Foliar fungicide use on hybrid corn has increased within the last decade, yet there are several questions pertaining to the value and sustainability of this practice. Field trials were conducted in Iowa, Illinois, Ohio, and Wisconsin from 2010 to 2012, using a split-split-plot experimental design. Main plots were hybrids varying in resistance to gray leaf spot and northern corn leaf blight. Subplots were four single applications of a quinone outside inhibitor fungicide at different timings. Sub-subplots consisted of inoculations with either <i>Cercospora zeae-maydis</i>, <i>Exserohilum turcicum</i> or both at two growth stages. Data were analyzed using PROC GLIMMIX in SAS. Mean disease severity was low (< 5% of leaf area affected) in 5 of 8 site-years. GLS-susceptible hybrids had significantly higher total disease severity (TDS), than resistant hybrids in Illinois (p<0.001) in 2010, Wisconsin (p=0.02) and Ohio (p=0.002) in 2010. Fungicide application significantly reduced TDS relative to the control in Illinois (p≤0.001) in 2010, Wisconsin (p=0.001) in 2011, and Ohio (p=0.02) in 2012. The susceptible hybrid had significantly lower grain yield than the resistant hybrid (p≤0.05), and the untreated control significantly lower yield (p≤0.05) than the fungicide-treated in three site-years. These results suggest that hybrid genetics (susceptibility to disease) and the prevailing environment are the biggest drivers of observed differences in disease severity and yield.